Fringe spacing inversely proportional to slit separation

Steps:

• Recall double-slit interference formula for fringe spacing: x = λL / a, where λ is wavelength, L is screen distance, a is slit separation.
• Note λ and L are constant, so x ∝ 1/a.
• As a increases, x decreases hyperbolically.
• Graph x vs. a shows inverse relationship, starting high and approaching zero.

Why A is correct:

• Option A depicts x decreasing as 1/a, matching the formula x = λL / a.

Why the others are wrong:

• B shows linear decrease, but relationship is hyperbolic, not linear.
• C shows constant x, but x varies inversely with a.
• D shows increasing x, opposite to the inverse proportionality.

Final answer: A